Vacuum circuit interrupting apparatus



July 25, 1933. D. c. PRINCE 1,919,937

VACUUM CIRCUIT INTERRUPTING APPARATUS Filed July 14, 1930 Inventor-z David C. Princs, y W 6 His AttoT-n ey.

Patented July 25, 1933 UNITED STATES PATENT OFFICE,

DAVID C. PRINCE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK VACUUM CIRCUIT INTERRUPTING APPARATUS Application filed July 14,

My invention relates to vacuum circuit interrupting apparatus.

The interruption of a high voltage circuit by a vacuum device, as a fuse or switch,

terminals of electrodes immediately upon opening of the circuit. That is, the dielectric strength of the vacuum gap must hold back the rapidly increasing voltage, or recovery voltage, across the circuit interrupter terminals upon interruption of the circuit. Otherwise, the interruption is of but short duration and arcing is reestablished. The critical value of the breakdown volt age for a given gap is uncertain and the dlelectric strength of the gap may fail under varying conditions. In vacuum circuit interrupting devices heretofore develo ed, the terminals of the interrupting devices, when in the open circuit position, are separated by the vacuum gap itself so that a voltage breakdown may occur directly between the electrodes to re-establish arcing.

It is a principal object of my invention to provide an improved vacuum or low pressure alternating current circuit interrupter which shall have means for reducing the probability ofvoltage breakdown between the electrodes of the interrupter when separated by a gap in vacuum.

In accordance with my invention a vacuum circuit interrupter is provided with one or more conducting grids or barriers arranged so as to be inter osed in the gap between the electrodes 0 the interrupter and free to assume any potential. In other words, the grids have no definite or fixed tential in the open circuit position of the interrupter and may therefore be termed floating with respect to the electrodes. I

' have foundthat in evacuated or low pressure envelopes having floating grids interposed in the gap between the electrodes, the breakdown voltage between the electrodes is appreciably higher than in the case of grids 1880. Serial, No. 467,717.

having a fixed potential or in the case of a clear gap with no grids. The explanation for this phenomena would appear to be in the characteristic difference between a voltage breakdown in vacuum, or a gas, as mercury vapor at low pressure, and a breakdown in air or other gas particularl subject to ionization. When a voltage reakdown occurs between electrodes separated within a hi hly evacuated envelope for example, the breakdown may be but momentary since there is no continued ionization in the path of the breakdown. In other words, the vacuum gap recovers its full dielectric strength ractically instantaneously. In the case of air or a like gas, on the other hand, the breakdown generally is permanent or of appreciable duration due to.

the continued ionization of the air. The ionized gas makes a good conductor between the electrodes so that the gap may not recover its full dielectric strength during the reversal of the voltage impressed across the same. Accordingly, in the event of a momentary breakdown between a grid and one anode, the voltage may collapse between the grid and that anode but the breakdown will not extend to the other anode due to the fact that the double voltage does not remain on the other gap for a sufficient len h of time. The probability of a com ete breakdown is thus very greatly reduced My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterise my invention will be pointed out with particularity in the claims annexed to and forming a part of this s ecification.

Re erring to the drawing, Fig. 1 is a view partly in section, illustrating a vacuum use embodying my invention and Fig. 2 is a view, partly in section, of a vacuum switch likewise embodying m invention.

The vacuum fuse illustrate in Fig. 1 may be of conventional type and comprises in the present instance a highly evacuated envelope 1 through which the electrodes or terminals 2 and 3 are sealed. The fuse envelope and electrodes are freed of occluded gases in any suitable manner so that the vacuum, which is as high as may be practically obtained, shall not be impaired by asses formed during circuit interruption. he electrodes 2 and 3 which are composed of material particularly suited for the interruption of alternating current or direct current, such as for exam le tungsten for direct current and a metal aving a low melting point as nickel or copper for alternating current, are interconnected within the evacuated envelo e by a fusible element 4 and are electrica ly connected exteriorly of the envelope to the terminal caps 5 and 6 secured in a well known manner to the envelope 1. The electrodes may likewise be provided with shields 2 and 3', respectively disposed adjacent the sealing-in portions oi the electrodes for protecting the same from injurious efiects of arcing.

For the urpose of increasing the efiective break own voltage between the electrodes 2 and 3 when the fusible element 4 has been vaporized or otherwise removed from the ap between the terminals there is provide means comprising the grids 7 and 8 arranged in the ga between the electrodes and spaced prefera ly equal distances with respect to each other and the electrodes. The grids 7 and 8 are in the present instance constructed ofwire mesh in the form of a disc although it shall be understood that the grids may comprise solid metallic discs as well.

When the fusible element 4 is ru tured or vaporized due to excess current, t e arcing between the electrodes, if contlnued, must form a plurality of arcs in series between the electrodes and grids. That is, the voltage breakdown of the gaps in series must be concurrent for the arc to persist. For the purpose of removing the conducting fusible element 4 from the gap in the event that t is not completely vaporized, suitable means as springs under tension (not shown) may be connected to. the fusible elementso as to withdraw the unva orized portions from the ids and from t 0 gap, and to this end the usible element 4 extends freely through the central portions of the grids and is not fixed thereto. The full voltage is, there-. fore, practically immediately, depending on the rate of voltage rise, impressed across the terminals 2 and 3 and the fuse, tending to cause voltage breakdown of the gap and consequent re-establishing of the current. However, due to the fact that a momentary voltage breakdown between one electrode and a grid adjacent the same may occur without necessarily causing breakdown of the other gap or gaps, the grids 7 and 8 are effective to increase the apparent dielectric strength of the space between the electrodes so that after the first current zero a hi her breakdown voltage would be requir to break down this space than is usually the case. Or, in other words, there is less probability of voltage breakdown between the electrodes for a given'terminal or applied voltage.

In the embodiment of my invention illustrated in Fig. 2 a vacuum switch, comprising a highl evacuated envelope 9 and relatively movable electrodes 10 and 11 having contact portions 12 and 13 at theadjacent ends thereof, is provided with a grid 14 of the character above described disposed in the envelope 9 between the contact ortions 12 and 13 of the electrodes. As in the previous instance, the switch envelope and arts thereof are freed of occluded gases an .the electrodes are composed of material most suitable for current interruption. The electrodes 10 and 11 are sealed at o posite ends of the switch through the fiexi le metallic bellows 16 and 17 so that the electrodes may be moved longitudinall in opposite directions away from the grid 14 during the circuit interrupting operation. The grid 14 is in the present instance provided with a conductin ortion 15 disposed centrally thereof w ie is engaged at opposite sides by the contact portions 12 and 13 when the switch is in the closed circuit position illustrated in Fig. 2. The circuit opening operation is effected b simultaneously moving the contacts 12 an 13 in opposite directions away from the grid 14 so as to form two gaps in series between the contacts. The

current is more readily interrupted at the in series with no ready communication or.

ionization established in one gap to the other t shall be understood of course, that my invention is not limited to any particular number of grids or barriers in the gap between the e ectrodes and that the character and number of lgrids may be chosen in accordance with t e articular operating re quirements involved? It shall be further understood that m invention is not limited to specific detai of construction and arrangement thereof herein illustrated, and that chan and modifications may occur to one ski led in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent .of the United States, is:

1. A vacuum alternating current circuit interrupter comprising a highly evacuated envelope, electrodes extending within and sealed with respect to said envelope, conducting means interconnecting sald electrodes in the closed circuit position of the interrupter, said electrodes being separated by a gap in vacuum in the open circuit posielectrodes extending through and sealed with respect to said envelope, a fusible element interconnecting said electrodes within the envelope, and a conducting grid interposed between the portions of said electrodes to which the fusible element is connected and arranged so that upon blowing of said fusible element a vacuum gap is created between each of said electrodes and said grid.

3. A vacuum, alternating current switch comprising a highly evacuated envelope,

electrodes, sealed and mounted for relative movement with respect to said envelope, said electrodes having contacts mova 1e within said envelope, and a conducting grid interposed between said contacts so as to form therewith two gaps in series between said contacts during opening movement of the switch.

4. A vacuum switch comprising a highly evacuated envelope, electrodes sealed and mounted for relative movement with respect to said envelope, said electrodes having contacts movable within said envelope, a conducting portion disposed between and interconnecting said contacts in the closed circuit position, and a conducting grid mounted in said envelope and connected to and supporting said conducting portion, said grid being separated from each of said contacts by a vacuum gap in the open circuit position of said switch.

DAVID C. PRINCE. 

